The present invention relates to connectors and, more specifically, to connectors for fiber optic cables.
The employment of fiber optic cables or light guides, also sometimes referred to as optical communication fibers, for the transmission of information-bearing light signals, is now an established art. Much development work has been devoted to the provision of practical low-loss glass materials and production techniques for producing glass fiber cables with protective outer coatings or jackets. The jacket makes them resemble ordinary metallic-core electrical cable upon superficial external inspection. Obviously, if fiber optic cables are to be used in practical signal transmission and processing systems, practical connectors for the connection and disconnection of fiber optic cables must be provided.
Before the prior art in respect to connectors, per se, is discussed, some references will be given for background in the state of fiber optic art in general.
An article entitled, "Fiber Optics," by Narinder S. Kapany, published in Scientific American, Vol. 203, pgs. 72-81, November 1960, provides a useful background in respect to some theoretical and practical aspects of fiber optic transmission.
Of considerable relevance to the problem of developing practical fiber optic connectors, is the question of transfer efficiency at the connector. Various factors, including separation at the point of abutment, and lateral separation or offset, are among the factors effecting the light transfer efficiency at a connector. In this connection, attention is directed to the Bell System Technical Journal, Vol. 50, No. 10, December 1971, specifically to an article by D. L. Bisbee, entitled, "Measurement of Loss Due to Offset, and End Separations of Optical Fibers." Another Bell System Technical Journal article of interest appeared in Vol. 52, No. 8, Oct. 1973, and was entitled, "Effect of Misalignments on Coupling Efficiency on Single-Mode Optical Fiber Butt Joints," by J. S. Cook, W. L. Mammel and R. J. Grow.
The patent literature also contains much information relative to the state of this art. For example, U.S. Pat. No. 3,624,816 describes a "Flexible Fiber Optic Conduit." The device described therein uses a plurality of light conducting fibers in a flexible cable-type arrangement.
Concerning the utility of fiber optic cables and therefore the utility of connectors for such cables, various systems are described in the patent literature which employs fiber optic cables. One example of such a utilization system is described in U.S. Pat. No. 3,809,908, "Electro-Optical Transmission Line."
Yet another patent of interest is entitled, "Glass Fiber Optical Devices," U.S. Pat. No. 3,589,793. This reference relates to the fiber optic bundles and the glass fibers themselves as well as to a method of fabrication for the fiber optic elements themselves.
A selection of U.S. patents relating more particularly to optical cable connectors includes U.S. Pat. Nos. 3,790,791; 3,734,594; 3,637,284; 3,572,891; 3,806,225; 3,758,189 and 3,508,807. These patents are representative of the connector prior art.
A fiber bundle-to-fiber bundle connector design requires the polished bundle ends to be positioned and held in close proximity. The most direct way to accomplish this is to butt the bundle ends together. When the ends of the fiber bundles are in abutting contact, repeated matings of the connector members in which the bundles are mounted and movement due to vibration can cause bundle surface scratching, especially when grit is present in the connector. The result is excessive light diffusion, causing optical losses at the abutting bundle interface. Losses due to surface scratching may amount to 4 dB or more. The purpose of the present invention is to provide a fiber optic cable arrangement which eliminates scratching of the end surfaces of the fiber bundles with optical power losses less than that which results from surface scratching.